A printing unit with two web guide elements, which two web guide elements are arranged respectively in an inlet and in an outlet area of a printing unit in such a way that, with the printing location disengaged, a web can be conducted through the printing location without touching it, is known from DE 93 11 113 U1. The two web guide elements are embodied as rollers, which are rotatably seated in lateral walls of the printing unit.
A turning bar is disclosed, in one preferred embodiment, in U.S. Pat. No. 3,744,693. A tube wall element made of a porous material which is permeable to air forms a closed pressure chamber in conjunction with a base body. The porous segment constitutes a wall of the chamber and is embodied to be load-bearing over the width of the latter, without a load-bearing support. In a second example, a segment with through-bores is utilized instead of the porous segment.
U.S. Pat. No. 5,423,468 shows a guide element which has an inner body with bores and an outer body of a porous material which is permeable to air. The bores in the inner body are only provided in the expected area of a loop of material which will pass around the guide element.
EP 0 705 785 A2 is concerned with the transport and deflection of web-shaped material, for example in the form of film material. In one embodiment, compressed air flows through the pores of a porous wall with mean pore diameters of 7 to 10 μm, and in another embodiment air flows through a wall having micro-bores with openings of 350 μm.